In my prior U.S. Pat. No. 5,640,952, the disclosure of which is incorporated herein by reference, there is disclosed a personal emergency breathing system for supplied air respirators. That system includes a canister closed at one end by a closure or cover and containing a filtration unit for filtering ambient air flowing through the canister. The canister includes a coupling for securing the canister to a face mask or an air supply line attached to the face mask and which face mask or supply line form part of a supplied air respirator. Typically, a supplied air respirator employs a face mask coupled to a supply of air, i.e., an air tank. The user, for example, a fireman, can thus breathe air supplied from the air tank when in an oxygen-deficient environment, for example, in a smoke or toxic fume-filled area. As set forth in my prior patent, the user of the supplied air respirator may unexpectedly encounter a malfunction of the supplied air respirator or the air supply may become exhausted at a time when the user is not able to leave the oxygen-deficient area. By immediately detaching the supplied air hose and regulator fitting from the face mask and attaching the canister to the face mask or to a portion of the supplied air hose attached to the face mask, the user is able to breathe filtered ambient air for a limited period of time, for example, on the order of about fifteen-twenty minutes. Under those circumstances, the user has that additional, though limited, time available to egress the toxic fume-filled area.
Not infrequently, however, after detaching the supplied air hose from the face mask or a portion of the supplied air hose, the user of the supplied air respirator has difficulty in attaching the canister to the face mask or the supplied air hose portion. When the canister is to be attached directly to the face mask, the canister may be out of the line of sight of the user, requiring the user to secure the canister essentially by feel, i.e., feeling the parts of the canister and face mask and manipulating them sight unseen to effect the connection. Even if the canister is to be attached to a portion of the supplied air hose in the user's line of sight, smoke-filled environments, for example, can prevent the user from observing the intended connection, thus delaying and possibly preventing the connection of the canister to the face mask or hose portion. In the event of a malfunction of the supplied air respirator or complete exhaustion of the supplied air, the user has only a very few seconds in which to effect the connection between the canister and the face mask or supplied air hose portion before being overwhelmed by toxic fumes. Thus, it has been found desirable to provide a locator on the canister for guiding the canister into quick securement with the fitting on the face mask or a supplied air hose portion of the supplied air respiratory system.
It has also been found with the foregoing-described system, as well as in the more general system set forth in my prior U.S. Pat. No. 5,315,987, the disclosure of which is incorporated by reference, that rough handling or vibration of the canister may have a significant effect on the filter materials of the filtration unit. In one form of filtration unit, the filter material is disposed in layers within the unit and preferably comprises a layer each of activated charcoal granules, a desiccant and a catalyst for catalyzation of carbon monoxide to carbon dioxide, each layer being separated by a fine fabric filter for collecting dust and particulate matter. Also, a layer of lithium peroxide or other suitable chemical may comprise a fourth layer of filter material for converting carbon dioxide to oxygen. In an alternative form, a ceramic monolithic catalytic filter may be provided. Rough handling, vibration or other quick displacements of the canister can introduce gravitational or inertial forces of sufficient magnitude to cause damage to the filtration material. For example, the ceramic substrate may crack or crumble or the filtration materials may start to move within the unit. Deterioration of the filtration granules, break through or channeling of air passages through the filtration material can decrease the effectiveness of the filtration. Consequently, it has been found desirable to shock-mount the filtration unit relative to the canister to minimize or eliminate those deleterious effects on the filtration materials.